Not Applicable
The present invention relates generally to relief devices for tanks containing high-pressure gases. More specifically, the present invention relates to relief devices for truck-borne compressed gas cylinders.
Various types of compressed gases are commonly transported in long, narrow cylinders, or xe2x80x9ctubes,xe2x80x9d mounted directly on a tractor trailer chassis or in a xe2x80x9cmodule,xe2x80x9d or a box frame containing the cylinders that is loaded onto a flat bed trailer. These truck-borne compressed gas cylinders are often required by law to be fitted with relief devices designed to relieve pressure from the compressed gas cylinders in the event of cylinder over-pressurization or fire. These relief devices are typically attached to each end of a cylinder and take two major forms: cluster-type relief devices (typically for hazardous gases) and angle-type relief devices (typically for non-hazardous gases). The present patent application deals with an improved form of an angle-type relief device.
In U.S. Pat. No. 5,832,947, entitled xe2x80x9cGas Shut-Off and Pressure Relief Valve for a High Pressure Gas Vessel,xe2x80x9d issued to Andrew Niemczyk, a pressure relief valve is disclosed. The disclosed pressure relief valve has a threaded body that engages the side port in fluid communication with the gas passage. The side port has a radially extending shoulder that seats an annular sealing ring. A rupture disc, made from brass, is pressed by the threaded body against the sealing ring. During operation, the rupture disc is strong enough to withstand normal gas pressures. Pressure from the threaded body on the sealing ring provides non-leak support. At high pressures, the rupture disc will deform and rip and allow for the venting of the gas.
In U.S. Pat. No. 4,269,214, entitled xe2x80x9cSafety Pressure Relief Device,xe2x80x9d issued to Calvin. C. Forsythe, et al., a safety pressure relief device is disclosed. The disclosed safety pressure relief device has a casing with a threaded connection and a concentric axial bore therethrough. The open end of the casing engages a concave-convex rupture disc which is ruptured with a knife means including a plurality of spaced cutting teeth. An annular outlet ring is connected to the casing by a continuous heli-arc weld. The weld also connects the rupture disc and the knife means to the casing.
FIG. 1 illustrates another prior art angle-type relief device and its attachment to a compressed gas cylinder. FIG. 2 is an exploded view of a prior art angle-type relief device. As shown in FIG. 1, the relief device 20 does not attach directly to the cylinder 10. Rather, the relief device 20 screws into a xe2x80x9cbullplugxe2x80x9d 30, which itself screws into the cylinder 10. Thus, the bullplug has two sets of threads: a set of male straight threads 32 that engage a reciprocal female set 12 in the cylinder; and a set of female pipe threads 34 that engage a reciprocal set of male pipe threads 24 on the relief device 20. Each set of threads on the bullplug represents a potential leak or failure point. Moreover, having the relief device screw into the bullplug, which in turn screws into the cylinder, means that the relief device protrudes farther from the cylinder than it would if the relief device screwed directly into the cylinder. This greater protrusion presents a greater opportunity for a shear of the relief device from the cylinder in the event of an accident, resulting in uncontrolled compressed gas leakage.
As shown in FIG. 2, the relief device comprises a valve body 21 and a washer 25, rupture disc 26, shear ring 27, adapter 22, membrane 28, and flare nut 23. The valve body comprises a main body coaxial with its associated compressed gas cylinder and an integral riser portion having an axis perpendicular to the main axis and the cylinder axis. The operation of the angle-type relief device is described belowxe2x80x94prior art angle-type relief devices and the present invention operate to relieve pressure in essentially the same manner.
FIG. 2 illustrates how the riser portion 21b protrudes beyond the outer diameter of the relief device main body 21a. This presents yet another opportunity for shear in the event of an accident, in this case the shear of the riser and the rupture disc away from the main body. As FIG. 2 illustrates, in the event of a riser portion shear, the rupture disc, adapter, and flare nut will separate from the main body, creating an unobstructed flow path from the cylinder through the main body and on through to the atmosphere through the sheared riser portion.
Therefore, a need exists for an angle-type relief device that couples directly to its associated compressed gas tank, rather than via a bullplug, thereby lessening the likelihood of 1) leakage past a threaded connection, and 2) relief device shearxe2x80x94and the associated uncontrolled leakagexe2x80x94in the event of an accident. Furthermore, a need exists for an angle-type relief device without a riser and associated rupture disc that protrude beyond the diameter of the device""s main body, and the consequent increased likelihood of riser shear and the associated premature and uncontrolled relief.
Accordingly, it is an object of the present invention to provide an angle-type relief device for compressed gas cylinders that attaches directly to its cylinder rather than threading into a bullplug. It is a further object of this invention to provide an angle-type relief device for compressed gas cylinders that reduces or eliminates the likelihood of the rupture disc shearing away from the main body in the event of an accident. Thus, the present invention features a larger diameter threaded connection that may be threaded directly into the cylinder in place of a bullplug. Moreover, the present invention""s rupture disc is recessed into the relief device main body, thereby greatly reducing or eliminating the chance of accidental shear. It is a further object of the invention to deduce and eliminate the leak path of the gas in the cylinder. Thus, the present invention features two welds, first the orbital rupture disk is welded to the spud assembly and second, the spud assembly is welded to the relief device.
The present invention is a relief device for a high-pressure gas container, comprising a main body having a generally uniform outer circumference that defines a bore. The bore is in fluid communication with an interior volume of the high-pressure gas container. Within the bore is a relief devicexe2x80x94typically a rupture discxe2x80x94that relieves to the atmosphere the container""s contents when the container reaches a certain pressure. The relief device is coupled to the high-pressure gas container via a threaded connection on the container.
In one disclosed embodiment, the bore comprises a primary bore coaxial with the main body""s main axis, and a secondary bore in fluid communication with the primary bore containing the rupture disc. The secondary bore and rupture disc are each located within the main body""s outer circumference. A spud assembly and a non-vent plug retain the rupture disc within the secondary bore. The non-vent plug has a bore which is in fluid communication with the secondary bore when the rupture disc is ruptured. Depending upon the gas in the container, the non-vent plug bore may be filled with a fuse metal, which is designed to melt at a pre-determined temperature, and that allows container relief in the event of bursting of the rupture disc.
A shear ring between the non-vent plug and the rupture disc facilitates the rupturing of the rupture disc.